In general, a continuous variable valve timing (CVVT) system continuously changes opening/closing timings by changing the phase of a camshaft in accordance with the RPM of an engine and the load on a vehicle.
An automotive CVVT system 101 in the related art, as shown in FIG. 1, includes: a crank angle sensor that senses a rotational angle of a crankshaft; a cam angle sensor that senses a rotational angle of a camshaft 104; a variable valve timing unit 150 that is connected to a side of the camshaft 104 by a timing belt and advances or retards the camshaft 104; and an ECU that controls an oil control valve 108 on the basis of signals from the crank angle sensor and the cam angle sensor so that oil is supplied to an advancing chamber 111a or a retarding chamber 111b of the variable valve timing unit 150.
Further, the variable valve timing unit 150 is composed of a stator 110 that is connected by a timing belt to receive torque from the crankshaft and a rotor 120 that is integrally coupled to the camshaft 104, has a vane shape, and rotates with respect to the stator 110.
A main chamber 111 divided into the advancing chamber 111a and the retarding chamber 111b by the rotor 120 is defined in the stator 110, so when oil is supplied to the advancing chamber 111a through the oil control valve 108, a phase difference is generated between the rotor 120 and the stator 110 and the camshaft 104 is rotated, thereby changing the timing of a valve.
Obviously, when oil flows into the retarding chamber 111b through the oil control valve 108, a phase difference opposite to the phase difference described above is generated between the rotor 120 and the stator 110, thereby retarding the timing of the valve.
The CVVT system achieves an effect of improving fuel efficiency, reducing an exhaust gas, increasing low-speed torque, and improving output by optimizing the opening/closing timing of valves of an engine in accordance with the RPM of the engine, and an effect of improving fuel efficiency by reducing a pumping loss by increasing valve overlap of intake/exhaust valves. Further, it has an effect of reducing an exhaust gas by re-burning a non-burned gas due to an internal EGR by optimizing the valve overlap according to engine conditions and an effect of increasing low-speed torque and improving output by increasing volume efficiency through optimization of the intake valve timing according to engine conditions.
Recently, an intermediate phase CVVT system improving a limit in response and operation range of the existing CVVT system has been actively developed.
FIG. 2 shows a most advance position, a parking position, and a most retard position of a cam in the intermediate phase CVVT system. The intermediate phase CVVT system, unlike the existing CVVT system, controls the position of a cam not at the most advance (intake) and most retard (exhaust) positions, but at a middle fixed position, so response is quick and the use range (operation range) of the cam can be increased, and accordingly, the fuel efficiency is improved and the exhaust gas is reduced.
However, the intermediate phase CVVT system has complicated internal channels and is required to precisely control an OCV (oil channel control valve).
In particular, as in FIG. 2, the CVVT electronically controls a locking-pin (solenoid ON/OFF control) through a separate solenoid valve in order to mechanically park a cam at the parking positions, except the area controlled in the advance/retard direction, in which when locking/unlocking of the locking-pin fails to be controlled, the locking-pin cannot be unlocked, so the CVVT cannot operate, and the locking-pin cannot be locked, the cam is oscillated.
That is, when a locking-pin cannot be locked/unlocked in an electronically controlled intermediate CVVT system, the CVVT fails to operate and the cam position at the parking position is oscillated, so response may be deteriorated, drivability may become poor, then engine may stop, and the engine may not start.
However, when the locking-pin fails to be locked, it is physically locked when cam torque and spring force become equilibrium in CVVT, so that the problem that the locking-pin fails to be locked due to cam torque can be solved by increasing the spring force, but the problem that the locking-pin is unlocked cannot be solved while the engine operates.
For example, an ECU controls a locking-pin in response to an electric signal from a solenoid valve, and it necessarily takes time to release the locking-pin (solenoid valve) by applying electricity to the solenoid valve.
However, when oil is supplied to a CVVT hydraulic circuit and the CVVT operates first, before the locking-pin is unlocked, the problem of locking of the locking-pin 1 is generated, as in FIG. 3, so that the locking-pin 1 is physically stuck and cannot be released.